1. Field of the Invention
The present invention relates to a liquid ejection head, and more particularly, to liquid ejection technology for a liquid ejection apparatus and head, which suppresses change in ejection characteristics due to change in the liquid temperature.
2. Description of the Related Art
An inkjet recording apparatus is known, which comprises an inkjet head (liquid ejection head) having an arrangement of a plurality of nozzles and which records images on a recording medium by ejecting ink from the nozzles toward the recording medium while causing the inkjet head and the recording medium to move relatively to each other.
In the inkjet recording apparatus, ink is supplied to pressure chambers from an ink tank, through an ink supply channel, and by driving actuators by supplying electrical signals corresponding to the image data to the actuators, the pressure chambers are caused to deform, thereby reducing the volume of the pressure chambers and causing the ink inside the pressure chambers to be ejected from the nozzles in the form of droplets. In the inkjet recording apparatus, a desired image is formed on a recording medium by combining dots formed by ink ejected from the nozzles.
In recent years, it has become desirable to form images of high quality on a par with photographic prints, in inkjet recording apparatuses. In response to this, the dots can be made finer and image resolution can be increased by reducing the size of the ink droplets ejected from the nozzles by reducing the nozzle diameter, and furthermore, increased resolution of the dots and improved quality of the image formed on the recording medium can be achieved by increasing the number of pixels per image by arranging the nozzles at high density. As a method of increasing the density of the nozzle arrangement, it has been proposed that nozzles be arranged in a two-dimensional matrix array.
It is generally known that, when the temperature of the inkjet head (the temperature of the ink in the inkjet head) changes, then the viscosity of the ink changes and the ink ejection characteristics vary. For example, the ink viscosity falls when the ink temperature rises, and the ink viscosity rises when the ink temperature falls. If the ink viscosity rises, then the volume of ink ejected when a prescribed pressure is applied becomes smaller than the prescribed ejection volume, and the speed of flight of the ink droplet is smaller than the prescribed speed of flight. The following methods have been proposed in order to achieve stable ink ejection, even if there is a change of this kind in the ink temperature.
One method of resolving the aforementioned problem is to measure the temperature of the ink (inkjet head) and to implement control whereby the ink temperature remains uniform. More specifically, there is a method in which the temperature is controlled by using special temperature control elements, or a method in which the actuators are caused to vibrate to generate heat used to control the temperature. On the other hand, a method is also proposed in which the drive waveform applied to the actuators is controlled on the basis of the measured temperature. More specifically, proposed methods include: a method which changes the ejection force generated by the actuators by varying the voltage of the drive waveform; a method which changes the frequency of the drive waveform (drive frequency) (Japanese Patent Application Publication No. 10-217465); a method which raises the temperature of the ink by driving the actuators at a high frequency (Japanese Patent Application Publication No. 11-99666); a method which varies the ejection timing; and the like. Furthermore, a method has been proposed in which a plurality of the methods described above are combined together and when the ink temperature is measured, the drive waveform of the energy generating members is controlled by heating and controlling the ink (Japanese Patent Application Publication No. 2003-136690).
However, in the methods described in Japanese Patent Application Publication Nos. 10-217465, 11-99666 and 2003-136690, and the like, temperature measurement elements to measure the ink temperature, and a control circuit for temperature measurement, are required. Furthermore, in a method in which the ink temperature is controlled so as to be uniform, then it is necessary to provide temperature control elements for controlling the temperature, and a control circuit and control system for driving these temperature control elements. In a method in which the drive waveform is controlled, a circuit or control system for altering the drive waveform is required. If a control circuit or control system of this kind is used, then not only do the head structure and the circuit composition become more complicated, but also, there is a probability of increasing the load on the control system of the head.